sedimentary

Stromatolite (Fossiliferous Limestone)

Biogenic Limestone (Calcium Carbonate, CaCO3)

Hardness: 3-4 (Mohs scale); Color: Gray, tan, or brown with darker organic bands; Luster: Dull to earthy; Crystal structure: Microcrystalline; Cleavage: None (conchoidal to irregular fracture); Specific Gravity: 2.5-2.7.

Hardness: 3-4 (Mohs scale)
Color: Gray, tan, or brown with darker organic bands
Luster: Dull to earthy

Identified February 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the trapping, binding, and cementation of sedimentary grains by biofilms of microorganisms, primarily cyanobacteria (blue-green algae), in shallow marine or lacustrine environments. These specimens often date back 500 million to 3.5 billion years.

Uses & applications

Used as decorative landscaping stone, architectural building stone, and highly valued by paleontologists and fossil collectors.

Geological facts

Stromatolites are the oldest fossils on Earth and represent the earliest evidence of life. They were responsible for creating the oxygen in Earth's early atmosphere through photosynthesis.

Field identification & locations

Identified by wavy, laminated, or 'cabbage-like' internal layering. In the field, look for weathered outcrops in limestone-rich regions like the Great Lakes (USA), Australia, or Canada. Bubbles when touched with diluted hydrochloric acid.

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